Heat stabilization of polyamide fibers bristles and foils

ABSTRACT

A PROCESS FOR THE HEAT STABILIZATION OF POLYAMIDE FIBERS, BRISTLES AND FOILS WITH COPPER COMPOUND, AREOMATIC AMINES, AND ALKALI, HALIDES. THE COPPER COMPOUND AND AMINES ARE INCORPORAED IN THE STARTING MATERIALS PRIOR TO THE POLYMERIZATION. THE ALKALI HALIDES AND ANY OTHER COMPONENTS OF THE STABILIZER ARE ADDED ONLY UPON THE FORMATION OF FIBERS, BRISTLES OR FOILS, PRIOR TO STRETCHING.

United States Patent US. Cl. 264-136 6 Claims ABSTRACT OF THE DISCLOSUREA process for the heat stabilization of polyamide fibers, bristles andfoils with copper compounds, aromatic amines, and alkali halides. Thecopper compounds and amines are incorporated in the starting materialsprior to the polymerization. The alkali halides and any other componentsof the stabilizer are added only upon the formation of fibers, bristlesor foils, prior to stretching.

This application is a continuation-in-part of copending application Ser.No. 666,931, filed Sept. 11, 1967, now abandoned.

The invention relates to the improvement of the heat stabilitycharacteristics of polyamides.

Linear polyamides produced, e.g., by polycondensation ofepsilon-aminocarboxylic acids, caprolactam (nylon-6), or ofhexamethylene diamine and adipic acid (nylon-66), have unsatisfactoryresistance to atmospheric oxygen at elevated temperatures.

Attempts have been made to increase heat stability by adding compoundssuch as lactams or diamine-dicarboxylic acid salts to the polymers or tothe starting products. Copper salts of inorganic or organic acids,combined with inorganic or organic halogen compounds, particularlyidoine compounds, have been found to be effective. Other additives whichmay be employed include for example phosphorus compounds, thioglycolicacid, chromium compounds, and certain aromatic amines, such asdi-beta-naphthyl-p-phenylenediamine, N-phenylbeta naphthylamine, or Nacyl p aminophenol, and especially mercaptobenzimidazole.

Difiiculties are encountered in the practical application of all ofthese combinations. Extraction of the lower molecular weightconstituents from the finished polymer is generally required. Additionof iodine and copper compounds to the starting products which form thepolyamides disadvantageously results in the major portion of the addedcompounds, especially the iodine compounds, being removed during theextraction.

A mixture of, e.g., a copper compound with alkali iodides in therequired concentration can be dusted on the extracted chip prior tospinning. While good heat stability thus is attained, the distributionof the stabilizers in the polyamides is not uniform. This leads to aconsiderable decrease in their strength characteristics, particularlywhen fibers, bristles and foils are produced. The reason for thisdrawback is that the stabilize components cannot be applied uniformlyeven when dusted. This is especially true in the presence of inorganichalogen compounds. Moreover, insoluble precipitates form in the melt,upon addition of the stabilizers to the polyamide forming startingproducts. Upon spinning, using either method of stabilizer addition, thestabilizer components precipitate at the outer edge of the spinningnozzles. Thus frequent changing of the spinning nozzles is required.Finally, a further disdvantage of dusting poly- 3,642,971 Patented Feb.15, 1972 amide formers with organic compounds in that very high thermalstability of these organic compounds is required. Therefore, a number ofeffective organic compounds, cannot be used due to their thermalinstability.

It is the obect of the invention to devise a method of stabilizingpolyamide fibers, bristles and foils with the compound named, whiledoing away with the drawbacks mentioned. This is accomplished by addinga first group of stabilizer components directly to the startingmaterials from which the polyamides are produced. These first componentsare copper compounds and organic nitrogen compounds, such as organicamines. The second component group, consisting of alkali halides and anyother material known for the purpose, is incorporated only upon shapingof the polyamides into fibers, bristles or foils, but prior to theirstretching. These second components are applied to the surfaces of thepolyamides in the form of solutions or suspensions.

In one embodiment, the second components are added to the spinningpreparations of the fibers or the like. This permits the stabilizers topenetrate into the interior of the freshly spun fiber since the spinningpreparation is applied to the dry and absorptive amorphous filament.This can be accomplished, e.g., by leading the filament through tworollers. It also is feasible to add the second component with otheradditives, such as light stabilizers, optical bleaches, and the like.This latter procedure has the added advantage that no specialoperational step is required and hence saves expenses.

The process according to the invention, as compared with processeswherein application occurs after stretching, also effects awash-resistant fixing of the second component on the fiber because thestretching operation following spinning leads to a compaction andorientation of the fiber structure whereby, due to the occurringcrystallization, the initially porous structure is closed and theaccessibility of solubilizing agent to the inner regions of the fibersis substantially decreased after stretching.

A desirable effect of the separate addition of copper compounds such aspotassium iodide to the starting materials and, is that theprecipitation of copper-I-iodide, which occurs upon simultaneousaddition is prevented. Precipitation of the copper compoundsprecipitation destroys the particularly effective stabilizing capacityof the copper salt and potassium iodide.

When the ingredients of the second components of the stabilizercombination are of mutually poor compatibility, i.e., when the differentcompounds together yield insoluble precipitates or when the storage lifeof the solution or emulsion is insufiicient, the two incompatibleingredients can be applied using two different sets of rollers.

In a further embodiment, the second components of the stabilizercombination are applied as an aqueous solution or in an organic solvent,to the spinning fiber on the first roller set. If desired, additionalsecond component may be applied by means of a second roller set. Thisenables an application in several layers, and incompatible ingredientswhich, however, are soluble in water or organic solvents, can beapplied.

Conversely, it is possible to apply the stabilizer component solely onthe surface of the fiber by using the first roller set for the spinningpreparation alone with the second roller set applying the stabilizer. Inthis manner, the stabilizer acts only on the surface of the fiber wheredamage caused by oxidation is the greatest. If undesirable side effectsof the stabilizer occur, due to catalytic chain disintegration, theseside effects will be limited to the fiber surface.

The invention now will be more fully explained by the followingexamples. However, it should be understood that these are given merelyfor the purpose of illustrating the invention and not for the purpose oflimiting same.

Further, it is intended to cover all modifications and variations whichdo not constitute a departure from the spirit and scope of the inventionas hereinafter claimed.

Percentages named in the examples are by weight, where applicable.Temperatures are in degrees centigrade.

The stabilizing effect of the combinations in the examples wasdetermined by subjecting the stretched fibers to the action of hot airat 160 for 48 hours in a circulating air oven. The stabilizing effectwas determined by ascertaining the percent decrease in specificviscosity of a 1% polyamide solution of 96% sulfuric acid. Aging tests,showing the percent decrease in tensile strength of the fibers, beingproportional to the lowering of the viscosity, were not carried out.

The examples are equally valid for fibers, foils and bristlesmanufactured as described.

EXAMPLE 1 0.03% copper-II-acetate. H and 0.13% mercaptobenzimidazolewere added to epsilonaminocaprolactam in a polymerization vessel. Chipsmanufactured by the polymerization were freed from oligomers byextraction with water, melted in a melt extruder at 270 and spun througha 34-hole nozzle to fibers of a total titer of 585 denier.

As a second stabilizer component, 80 g./l. aqueous KI solution wereapplied to the spinning preparation by conducting it through tworollers. The amount of potassium iodide corresponded to an iodinecontent of 0.1, calculated on the weight of the fibers. The yarn thusobtained was then stretched in proportions of 1:3.505 over a heatedstretcher.

The decrease in specific viscosity, measured as described above, was

Polyamide chips, produced from episilonaminocaprolactam having asolution viscosity of 1.94 (0.5% solution in m-cresol) were powderedwith a mixture of 0.03% copper-I-chloride and 0.13%mercaptobenzimidazole, calculated on the weight of the chips. Themixture had been ground to a fine dust. Spinning and stretching werecarried out as in Example 1, but without addition of KI to the spinningpreparation. The specific viscosity drop was 6%.

We claim as our invention:

1. In a process for heat stabilizing a polyamide fiber, bristle or foil,produced by polymerizing, starting materials selected from the groupconsisting of epsilonamino carboxylic acid and caprolactam, andhexamethylene diamine and adipic acid to produce a polyamide thenspinning and stretching same, said heat stabilizing being accomplishedby adding to said polyamide a compound selected from the groupconsisting of heat stabilizing copper salts, organic aromatic amines andmixtures thereof, and a heat stabilizing alkali halide, the improvementwhich comprises incorporating said compound with the starting materialsprior to their polymerization and applying said alkali halide to thesurface of said produced polyamide upon the spinning of same into afiber, bristle or foil and prior to the stretching.

2. A process as defined in claim 1 wherein said alkali halide ispotassium iodide and the amount of said potassium iodide applied to thesurface of the produced polyamide corresponds to an iodine content of0.010.5% calculated on the weight of the fiber, bristle or foil.

3. A process as defined in claim 2 wherein said potassium iodide isapplied in the form of an aqueous solution or suspension.

4. A process as defined in claim 1 wherein said compound is a mixture ofa copper salt and mercaptobenzimidazole and said alkali halide ispotassium iodide, said copper salt being present in an amount ofsubstantially 0.010.1% by weight calculated on the materials to bepolymerized, said mercaptobenzimidazole being present in an amount ofsubstantially 0.01-0.13 weight percent and said potassium iodide ispresent in an amount which corresponds to an iodine content of 001-05weight percent calculated on the weight of the fiber, bristle or foil.

5. The process as defined in claim 1 wherein said copper salt iscopper-III-acetate.

6. The process as defined in claim 1 wherein said copper salt iscopper-I-chloride.

References Cited UNITED STATES PATENTS 2,630,421 3/1953 Stamafott260-458 2,705,227 3/1955 Stamafott 260-45.7 2,945,010 7/1960 Caldwell etal 260- 3,275,594 9/1966 Bond 264-211 3,282,892 11/1966 Griehl 260-45753,308,091 3/1967 Zapp 260-785 C 3,318,827 5/1967 Whittker 260-183,459,702 8/1969 Tazewell 260-785 C JAY H. WOO, Primary Examiner US. Cl.X.R.

117-7, 138.8 N; 260-457 R, 45.75 C, 45.9 R, 45.8 N, 78; 264-210 F, 211

